In the past, we reviewed the Pass Labs XP-20 and XP-30 stereo preamplifiers. Now, we come full circle with a review of the remaining member of their preamplifier trio, the XP-10, which is the least expensive model. It is fully balanced, and has a slightly different sound character compared to the other two, which also sound different from one another. All three are great products, so you can choose based on price and/or sound characteristics.

SPECIFICATIONS

Design: Fully Balanced Stereo Preamplifier

Maximum Voltage Output: 20 Volts RMS

MFR: 2 Hz - 60 kHz, - 3 dB

Inputs: Two Pairs XLR (Inputs 1 and 2), Three Pairs RCA (Inputs 3, 4, and 5; Input 5 is for Home Theater Pass-through with Unity Gain)

The XP-10 is a fully balanced solid state preamplifier. It has two gain stages and operates in pure Class A. There is no global negative feedback. The overall design results in the minimum amount of circuit path, which keeps signal loss at the lowest possible level.

It is said that the XP improvements over the previous model include deeper bass and better detail.

The front panel has buttons from left to right for Mute, Mode (Dims the LED Panel), and Input Selector. The large volume control (I have big hands and really appreciate big volume control dials) is on the right hand side, and it can be spun continuously, changing the volume through an optical encoder. It reads from 0 to 83, in 1 dB steps, with 75 being unity gain. The pass-through connection using input 5 sets the volume at 75 so that whatever SSP processor voltage that passes through to the power amplifier will be very close to what it was going into the XP-10.

The rear panel is shown below.

On the far left is the grounded AC receptacle. Most of the panel is occupied by the inputs and outputs. From the left is one pair of RCA outputs, one pair of XLR outputs, the Pass-through RCA input pair, two more pairs of RCA inputs, and two pairs of XLR inputs.

The remote control is the same one used for the XP-20 and XP-30. Simple, attractive, functional.

At 67, I still listen (and play along with) to rock music. I am not so much a fan of the metal genre, but rather the 80's era, including especially Van Halen. They were part of the bridge from classic rock to heavy metal, and the music had a melody - played with the volume controls to the max.

Most of my favorite Van Halen tracks are on Van Halen Best of: Volume 1.

"Jump" and "Dreams" in particular set my rock & roll afire. Eddie Van Halen on lead guitar and Alex Van Halen on the drums made the walls vibrate, through the XP-10. Guitar played through sound effects circuits (they produce various types of what would be best called distortion), and the way Alex crashed his cymbals, delivered a sound that was filled with high frequencies, but the only distortion that I could hear was the sound from those special effects boxes. Cymbals in particular, are difficult to reproduce without sounding harsh when played hard. Alex played them so hard, his knuckles are now enlarged from arthritis, and he is almost completely deaf (ear plugs for hearing protection were not standard in those days). Through the XP-10, the crashes were detailed and crisp, without a hint of harshness.

Even if you are not a fan of classical music, you would very likely recognize the opening bars of Edvard Grieg's Piano Concerto in A minor, Opus 16. Piano played at any volume is a tough cookie for an audio system, partly because we all know exactly how a piano sounds, so any deviation is immediately noticeable. Secondly, the lowest note has a fundamental frequency of 27 Hz. And when it is played fff, as it is in the opening bars, the cookie becomes even tougher. But not too tough for the XP-10. When the pianist pounds out the notes, there are very intense transient peaks at the beginning of the tone as the hammer strikes the metal piano wire, and I wondered if the XP-10 could handle it. No disappointment there. The symphony orchestra also came through loud and clear, with all the instruments distinguishable while the pianist (Clifford Curzon) did his thing. This is a manifestation of low IM distortion, which you will see in the bench tests.

Want another difficult instrument to reproduce? Try the violin, especially the instrument made by Guameri del Gesu in 1737 (I imagine one could trade that for quite a few lattes at Starbucks®.) So, on this Virgin Classics disc, Capriccio, Renaud Capucon (violin) and Jerome Ducros (piano) duke it out with 21 pieces by Schubert, Dvorak, Debussy, Prokofiev, Stravinski, Tchaikovsky, and others.

Well, the music just soared on the XP-10. My ears are very sensitive to any high frequency distortion, but by this point (I had listened to about 20 CDs and SACDs), I wasn't expecting anything but beautiful sounds and glorious music. It's a hard job testing masterpieces of electrical engineering like the XP-10, but someone has to do it. I volunteer to continue along the road.

I also listened to the XP-10 using a pair of HiFiMAN HE-500 headphones, which allows me to discern differences between preamplifiers where there are subtle differences, as there were between the XP-10, XP-20, and XP-30, all of which I have reviewed. I connected the HE-500 headphones to the XP-10 preamplifier using the RCA outputs and a stereo RCA plug - 1/4" phone jack adapter cable.

I would classify the sound of the XP-10 as neutral with just a dash of warmth. See the Conclusions section for more info on the differences between the three Pass preamplifiers.

On the Bench

Distortion measurements were made within an 80 kHz bandwidth. The XLR inputs and outputs were used for all tests, and the volume control was set to 75 (unity gain, i.e., input voltage delivers the same output voltage, or close to it). I adjusted the input voltage for each test to produce 2 volts RMS output (except where noted).

At 1 kHz, there was a scant 0.001% THD+N. The second order harmonic is predominant. This is exquisite performance. The spectrum is different than the XP-20 and XP-30, where the third order harmonic was a bit higher than the second order harmonic.

At 19 kHz and 20 kHz, there were only two side-bands (the peaks on either side of the 19 kHz and 20 kHz peaks), and the B-A peak at 1 kHz was 105 dB below the fundamentals.

IMD was extremely low, at 0.001%. This is what gave me that clarity with the full symphony orchestra. Low IMD means no mushiness in the midrange, which would otherwise throw a towel over the music.

THD+N vs. Frequency is shown below. At 2 volts output, the curve is nearly flat, and even at 5 volts output, the curve rises at 20 kHz only to a bit less than 0.01% THD+N.

Here, we see THD+N vs. Output Voltage (the volume control was set to 75 - Unity Gain). With a 100 kOhm load, the soft knee was at 4 volts, the hard knee at 13 volts, and clipping at 15 volts. With a 600 ohm load, the output drops. One would never encounter a 600 ohm load under normal circumstances. This is just a stress test.

The measured frequency response was 20 Hz - 20 kHz, - 0.5 dB.

Conclusions

So, I have reviewed all three of Pass Labs' stereo preamplifiers. All of them perform beautifully, and each one has its own sonic personality, but the differences are subtle. As I mentioned in my review of the Pass Labs XP-30, "I would pair the XP-20 with a tube power amplifier, and the XP-30 with a solid state power amplifier." The XP-10 seems to be the most neutral of the trio, so you could pair it with either tubes or solid state power amplifiers. Thus, take your choice, behind Door # 1, Door # 2, or Door # 3. Don't worry. A terrific prize is behind each door.